In prior-art arrangements of the type mentioned by way of introduction, the locking tongue has a double function by serving as guide means as well as locking means, the hook member arranged thereon being adapted to cooperate with the main section or with a second locking tongue arranged from the opposite direction and belonging to a second transverse section. The rigidity of the locking tongue is considerable, in many cases by the locking tongue being formed with embossed portions, longitudinal beads or the like. As will be appreciated, this affects the resilience of the locking tongue in a negative way, which makes it difficult to mount and dismount a transverse section. Moreover a remaining deformation of the locking tongue often arises when bending it laterally outwards, as is required in mounting and dismounting. Such deformation is, of course, disadvantageous and may cause, among other things, an inaccurate positioning of the associated transverse section.
A further problem is that prior-art designs of the locking tongues in many cases involve such a length of the locking tongues that after mounting in a main section, they protrude significantly on the side of the-main section facing away from the mounted transverse section. This is particularly unfavourable when a single transverse section is to be connected, i.e. when there is no second transverse section aligned with the first transverse section on the opposite side of the main section.
In the latter case of connecting a single transverse section, the positioning will, as a rule, be more inaccurate owing to the locking tongue being movable in the connecting hole which is generally formed to receive two locking tongues